The present invention relates in general to vehicle headlamps and in particular to the type of headlamp which has a parabolic reflector and cover lens.
Conventional vehicle headlamps typically include some type of filament, a parabolic reflector base and a molded lens sealed thereto in order to create an evacuated chamber. The atmosphere of this evacuated chamber surrounds the filament and the operational characteristics of the lamp (i.e., average life and candlepower) are directly influenced by the nature of this inner atmosphere.
In this inner atmosphere is not evacuated to a level sufficiently below one atmosphere when at "room temperature," then as the filament conducts current and heats the interior of the evacuated chamber, the gases filling this chamber expand to an excessive pressure level. While one solution to this potential problem is to evacuate the inner chamber to a lower pressure level, this option is offset by the fact that some inner atmosphere is needed in order to provide a suitable heat conductor surrounding the filament. The choice between the two "solutions" becomes a compromise in lamp construction wherein the initial chamber atmosphere is evacuated to a pressure level low enough to permit expansion to an allowable inner pressure when the lamp is at maximum operating temperature.
A related concern to that of an evacuated inner chamber is the need to void the interior of moisture and seal therewithin the particular gases selected for the interior atmosphere. The greater the pressure difference between the inside and outside atmospheres, the greater will be the demands placed upon the seal locations, and consequently, the more susceptible the assembly will be to leakage and thus failure.
One means to improve upon the foregoing problems is provided by the present invention wherein an expandable membrane is arranged in cooperation with the inner chamber of the lamp in order to accommodate volumetric expansion during operation. The membrane serves as an interface between two atmospheres of equal pressure. Although there is a variety of known prior patents which pertain to lighting and lamps, no reference is known to exist which reveals any concept that is related to the expandible membrane concept of the present invention.
A related aspect of the present invention pertains to the design of the filament and the use of a ceramic glow bar in order to increase the luminance and candlepower of the source. While glow bar concepts are known to exist, the present invention provides a design which is a practical, high production means of fabrication, its actual configuration, and its combined use with the disclosed ambient pressure lamp incorporating the expandable membrane.
Listed below are various patent references which are known to the inventor and which disclose lamp designs and related concepts. Consequently, these references may be relevant to the present invention, but none of the references are anticipatory of the present invention nor render the present invention obvious.
______________________________________ Pat. No. Patentee Issue Date ______________________________________ 1,406,645 Heany 2/14/22 1,640,829 Heany 8/30/27 1,749,136 Heany 3/04/30 1,975,499 Braselton 10/02/34 2,007,926 Braselton 7/09/35 2,901,654 Myers 8/25/59 4,032,809 Corth 6/28/77 4,146,812 Gagnon 3/27/79 3,027,481 Baber et al. 3/27/62 2,950,413 Jayne et al. 8/23/60 2,007,945 Harding, Jr. 7/09/35 1,623,761 Skaupy 4/05/27 2,273,762 Reerink et al. 2/17/42 ______________________________________
Heany ('645) discloses an incandescent electric lamp having a particularly styled filament. The filament includes a first helical coil of refractory metal disposed over a refractory compound. Additionally, there is a second coil providing an outer layer of turns disposed over a second layer of a refractory compound. To the extent that this particular invention pertains primarily to the construction and materials of the filament, it may have some relevancy to the present invention. Otherwise, the remainder of the lamp is in no way relevant.
Heany ('829) discloses an incandescent electric lamp, and in some regard similar to the first Heany reference, the invention focuses almost totally on the construction of the filament. In particular, a large number of arrangements are disclosed, all relating to the disposition of a tungsten coil relative to a refractory compound which supports the coil and possesses great strength at the operating temperature and is capable of becoming highly incandescent at the operating temperature of the lamp.
Heany ('136) discloses an incandescent electric lamp, again of the same basic idea and concepts of the earlier two Heany references. Here again, the invention focuses almost totally on the design and construction of the filament and the relationship of the tungsten coils to the refractory compound.
Braselton ('499) discloses a constant illumination electric lamp wherein the main thrust of the invention pertains to the arrangement of the filament which, in this case, is disposed between two support rods and includes a filament coil disposed around a rod of refractory metal and between the two support rods.
Braselton ('926) discloses a light-emitting unit wherein four support rods are provided and two coils. The two coils are arranged in a double-coil design such that two of the support rods support one coil and the other two support rods support the other coil. Both coils are disposed about a core of electron-emitting material in order to provide the desired illumination and candlepower for the light-emitting unit. Again, this particular invention pertains almost totally to the design and construction of the filament.
Myers discloses an electric incandescent lamp of the self-contained reflecting type which is adapted to project a beam of light. Additionally, the invention pertains to improvements in lamps of this type which are shatter-proof and to techniques for fabricating such lamps. The lamp assembly includes a Mangin mirror which is secured at its periphery to one end of a cylindrical metal shell. The other end of the shell is enclosed by a transparent window plate in order to form an evacuated chamber which contains the light-emitting element. The shell is constructed with inwardly turned edges in order to form a bellows-type of configuration at which point it provides a glass-to-metal seal. The fact that this shell is formed of a durable metal eliminates any suggestion or possibility that the interior volume is permitted to expand outwardly by expansion of the shell.
Corth discloses a coiled incandescible filament which principally comprises tantalum carbide and which has coiled end portions overfitting relatively thick tantalum carbide members. The inner surfaces of the overfitting coils are welded to the relatively thick members. Electrical connection and support for the filament is made to the relatively thick, overfitted members, rather than the fine, brittle filament.
Gagnon discloses a motor vehicle headlight which includes a curved reflector having a lens bonded to the front thereof and a tungsten-halogen capsule disposed within the reflector. A filling hole extends through the rear of the reflector and this hole is hermetically sealed by means of a nonrigid sealing material.
Baber et al. discloses in general a projection lamp and in particular to incandescent lamps that may be used in various devices utilizing an optical system in the projection of slides, motion picture films, or other types of transparent or semi-transparent objects. In particular, the lamp disclosed is intended to be acceleration and vibration-resistant and includes a filament in the form of a pair of semi-circular segments which are carried and supported by a generally cylindrical support element which in turn is held in position relative to the lamp by a plurality of rod-like supports.
Jayne et al. discloses a filament connection for electric lamps and similar devices and in particular relates to the connection between the filament and the leading end conductors. Although the patent discloses some specifics regarding the filament design, the primary nature of the invention is the connection concepts which are disclosed.
Harding, Jr. discloses an electric lamp with a concentrated light source and includes a pair of support rods holding a filament. The filament constitutes the primary aspect of the invention and is disclosed as including a cylinder of refractory material which is provided with a helical groove and an electron-emitting element which is made into a coil form and wound into the grove.
Skaupy discloses an electric glow lamp design wherein the support element which is normally made of refractory material is made of transparent material which will convey sufficient heat to the light-giving element mounted thereon in order to make the element luminous, yet the body in which the element is mounted does not interfere materially with the radiation of the light-giving element thereby enabling the light-giving element to stand out. This particular patent reference is believed to have very limited applicability to the present invention.
Reerink et al. discloses an incandescible cathode construction wherein one or more thin metal wires is wound around a metal core made of refractory material in order to form a structure in which a comparatively large mass and large area of a highly electron-emissive substance surrounds the core and is securely retained by the turns and/or layers of the thin wire. The purpose of this particular invention is to generate a very large emitting surface that can be provided on the cathode with an ample supply of emissive substance, which substance at the same time firmly adheres to the cathode.
A concept related to the invention of an ambient pressure lamp is the ability to reconfigure the front lens. When there is an internal pressure within the lamp, a convex outer lens is preferred from the standpoint of overall strength. In order to fabricate this convex shape, a molded glass construction is typically employed; but a plastic lens cemented to a reflector is one option. One drawback with the use of such plastic is the fact that it is more susceptible to the elements of weather and to chemicals. Once the plastic is scratched or begins to deteriorate due to the chemicals, light transmission is reduced.
One solution to this drawback is to use a lens with a flat outer surface and to fabricate this outer surface of a more durable material such as, for example, a thin overlay of glass. An inner layer of plastic can still be used for lens focusing, but a flat layer of glass on the outer surface provides the needed protection from the elements and chemicals. The fact that the interior of the lamp is at ambient pressure permits the use of a flat lens because the strength requirements for the lamp are greatly reduced since the internal lamp pressure of the present invention equals the external ambient pressure.